The present invention relates to the control of peripheral systems employing a plurality of devices and control unit(s); particularly the controls are those facilitating multipath access and subsystem integrity through the use of a hierarchical group control methodology and apparatus.
Peripheral systems attachable to hosts or central processing units (CPUs) have a critical relationship to total data processing system performance. It is essential for high performance that the peripheral systems attached to a host or plurality of hosts provide rapid access to the devices for performing a plurality of data processing operations. Additionally, to ensure control of the data processing operation, the peripheral system should provide integrity of the data processing operation; this aspect is particularly important when multi-users are time sharing the peripheral system.
In plural unit/device configurations, such as used in multiprocessor data processing installations, configuration control has been used for providing integrity and performance enhancement. For example, Stafford U.S. Pat. No. 3,386,082 relates to configuration control of a multiprocessor environment. FIG. 4 of that U.S. patent shows a tape control unit TCU capable of responding to configuration control commands received from a host. Each host in the Stafford patent has a configuration control register CCR which controls the flow of signals with respect to the host. Each unit communicating with any other unit has a configuration control register which allows or inhibits that particular unit/device from communicating wsith another particular unit. Hence, this U.S. patent teaches logical configuration control which can also be termed logical partitioning. While this patent does show a high degree of flexibility, a greater integrity control at low cost is still needed for peripheral systems, such as storage systems employing tape or disk type magnetic recorders.
Enhanced accessing of devices of peripheral systems can be achieved by multipathing. An example of this is shown in the document incorporated by reference, U.S. Pat. No. 4,207,609, which teaches the concept of path groups with a memory in the peripheral system for enforcing the path group concept of multipathing. The path grouping of this latter identified patent, while enhancing multipathing, does not provide for long term control of a peripheral system as may be desired for system integrity purposes.
Accordingly, it is desired to extend the multipathing control while maintaining a high degree of integrity in the peripheral system.
Other approaches to providing control of peripheral systems include the concept of a so-called logical channel in U.S. Pat. No. 4,060,849. This later patent does not show the concept of path grouping, thereby limiting control flexibiltiy at the peripheral system level. Additionally, permissive coupling of different subsystems have been employed, see U.S. Pat. Nos. 3,768,074 and 3,812,469. Such permissive coupling, as taught in those patents, appears to be achieved in processing groups of elements by transmission of system configuration codes and validation signals. These patents appear to be a sub-group of the teaching in the Stafford patent, supra. Further, logical partitioning of a multi-unit data processing system is shown in U.S. Pat. No. 3,641,505 which has a specific partition, apparently another subset of the Stafford teaching.